The present invention is directed to a system for sensing a signal in the primary side of a luminous lamp load driving circuit to detect an end-of-life lamp condition and provide for an adjustment or shut down of the load driving circuitry. More particularly, the present invention is designed to detect the transients across the direct current choke associated with an end of lamp life condition in order to provide a shut down signal for the load driving circuitry.
Ballasts using direct current chokes are known in the art. For example, U.S. Pat. No. 5,877,592 entitled Programmed-start parallel-resonant electronic ballast discloses a ballast having a direct current choke. In addition, patents describing protection circuits capable of detecting end-of-lamp-life conditions in lamps are known in the art. Examples of these circuits are described in U.S. Pat. No. 6,127,786 entitled Ballast having a lamp end of life circuit, U.S. Pat. No. 5,808,422 entitled Lamp ballast with lamp rectification detection circuitry, U.S. Pat. No. 5,777,439 entitled Detection and protection circuit for fluorescent lamps operating at failure mode, U.S. Pat. No. 5,635,799 entitled Lamp Protection Circuit For Electronic Ballasts, U.S. Pat. No. 5,606,224 entitled Protection circuit for fluorescent lamps operating at failure mode, U.S. Pat. No. 5,574,335 entitled Ballast containing protection circuit for detecting rectification of arc discharge lamp, U.S. Pat. No. 5,475,284 entitled Ballast containing circuit for measuring increase in DC voltage component, U.S. Pat. No. 5,142,202 entitled Starting and operating circuit for arc discharge lamp, U.S. Pat. No. 5,138,235 entitled Starting and operating circuit for arc discharge lamp, U.S. Pat. No. 5,111,114 entitled Fluorescent lamp light ballast system, U.S. Pat. No. 5,023,516 entitled Discharge lamp operation apparatus, and U.S. Pat. No. 4,429,356 entitled Transistor Inverter Device. Each of these patents is hereby incorporated by reference.
These patent teach different sensors in an electronic ballast, but fail to teach the use of a sensing circuit coupled to the dc choke for detecting the end of life condition. What is needed, then, is a Transient Detection of End of Lamp Life Condition Apparatus and Method.